The present invention relates generally to optical switches and, more particularly, to microelectromechanical optical switches and methods of manufacturing such optical switches.
Relatively modern technology now enables microelectromechanical systems (MEMS) to be fabricated on semiconductor substrates, typically silicon substrates. These microelectromechanical systems typically have sizes on the order of microns and may be integrated with other electrical circuits on a common substrate. As a result, microelectromechanical systems have found their way into numerous applications across numerous disciplines. Illustrative MEMS applications include optical switching, inertial or pressure sensors, and biomedical devices, for example.
MEMS-based optical switches are used in a variety of applications for switching light waves between optical waveguides, such as fibers. Present MEMS-based optical switches can operate in the plane of the substrate or normal to the substrate. An example of an in-plane optical switch using a vertical mirror is disclosed in C. Marxer et al., xe2x80x9cVertical Mirrors Fabricated By Reactive Ion Etching For Fiber Optical Switching Applications,xe2x80x9d Proceedings IEEE, The Tenth Annual International Workshop on Micro Electo Mechanical Systems, An Investigation of Micro Structures, Sensors, Acuators, Machines and Robots (Cat. No. 97CH46021), IEEE 1997, pp. 49-54. The Marxer optical switch includes a metal coated silicon mirror coupled to a dual comb drive actuator. The two comb actuators work in opposite directions to push the mirror into an optical path between optical fibers and to pull the mirror out of the optical path. The Marxer optical switch is fabricated in a single step using inductively coupled plasma etching technology with a sidewall passivation technique.
The Marxer switch is associated with a number of limitations. For example, its dual comb actuator requires power in both an extended position and a retracted position. Without power, the mirror undesirably lies midway between the fibers. In addition, while the Marxer fabrication technique provides walls with a verticality of 89.3xc2x0 and surface roughness of 36 nanometers (nm) rms (root means squared), room for improving each of these characteristics exists. Conventional DRIE and photolithography techniques, relying on oxide masks and ultrasonic mask removal, also have deleterious effects on MEMS structures. For instance, these photolithography techniques often leave debris between structures. Accordingly, improvements in optical switches are desired.
The present invention generally provides a MEMS-based optical switch having improved characteristics and methods for manufacturing the same. In accordance with one embodiment of the invention, an optical switch is provided which includes a single comb drive actuator including a stationary comb mounted on a substrate, a movable comb interleaved with the stationary comb, and a beam structure connected between the substrate and the movable comb and a mirror coupled to the actuator. The optical switch further includes a pair of first waveguide channels and a pair of second waveguide channels disposed on the substrate. The mirror is capable of being moved between an extended position interposed between the waveguide channels and a retracted position apart from the waveguide channels. The two combs apply a force capable of deflecting the beam structure and moving the mirror to one of the extended positions or the retracted position and the beam structure returns the mirror to the other of the extended position or the retracted position in the absence of the application of force between the two combs.
In accordance with another embodiment of the invention, a method forming a mirror on a substrate is provided. The method includes forming, over the substrate, a patterned masking layer covering the first region of the substrate and two side regions of the substrate each adjacent a side of the first region. After forming the patterned masking layer, uncovered portions of the substrate are removed using the pattern masking layer to form a first raised structure in the first substrate region and a sacrificial raised structure in each side substrate region adjacent the first raised structure. The sacrificial raised structures are then selectively removed while leaving the first raised structure intact and a reflective surface is formed on the first raised structure.
In accordance with another embodiment of the invention, a method of forming combs for a comb drive actuator on a substrate is provided. This method includes forming multiple layers of the same photoresist material over the substrate to form a composite photoresist layer. The photoresist material may, for example, be photoresist S1818. After forming the composite photoresist layer, the composite layer is patterned and developed to form a patterned photoresist layer having an interleaved masking pattern. Using the interleave masking pattern, portions of the substrate are removed to form interleaved combs. The process of forming the multiple layers may, for example, include depositing each layer of the photoresist material and heating the layers after deposition. The use of a multiple layer of a photoresist material, such as S1818, can, for example, enhance the surface roughness and cleanliness of the resultant structure as compared to other types of masking layers.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.